Hello folks.
I have some problems with two of my screws. They are in the end of each lineup. Sometimes, I have not been able to find any regularity, they stop from high oiltemperature. They have oilcoolers with NH3. The temperature is jumping, sometimes to get so high the compressors stops.
There is no oil in the liquidline nearby the oilcooler. There is no air in the system.
Anybody here seen the same? And most important: Anybody here have a suggestion what to do about it?
If you need additional information about my plant, please say so.

RANGER1

18-09-2015, 11:29 PM

Marthe,
Please find some questions

- You indicate screws on end of line up. How many screws are in between working OK?
- Ensure you have a constant good working level of refrigerant in thermosyphon receiver, what level do you have & can you physically see it clearly.
- Ensure condensing pressure is reasonably stable to avoid sudden pressure changes in thermosyphon system.
- What type of oil coolers, shell & tube or plate heat exchanger?
- Is it a new problem, or ongoing since new, or changes to plant recently?
Pipe work sizing may be inadequate.

- Does NH3 return line from oil coolers slope upward to avoid gas pockets?
Where does it return to, thermosyphon vessel, or discharge line before condensers.
- Have you tried restricting liquid to other thermosyphon oil coolers to favour ones that are not working?
- Does problem happen at certain times, or all the time?

If all else fails call Tycho

marthe1994

24-09-2015, 11:20 PM

I might have found the answer to my problem. It seems the two compressors stops after a sudden drop of condensing pressure. Not much, only 0,2-0,3 bars. But it seems like it is enough to make the oiltemperature rise.
I had some difficulties making condensing pressure stabil. I have seawater-cooling, and a condenser with water and fans.
I just turned the fans on manual (on all the time) and then I regulated cond.press. with seawater.
This seems to work. I don`t get pressurefall as the fans starts.
These two compressors stopped several times every hour. After my regulations they have been running nice for more than one hour. I pray and hope...

RANGER1

25-09-2015, 09:05 AM

Some plants can be sensitive for various reasons.
Sudden pressure drop can be described as lemonade effect on the ammonia (a lot of gas bubbles formed).
Sounds like a good approach with situation you have, good luck.